We propose to develop a novel testing platform to enable rapid, ultrasensitive, accurate, user-friendly, and cost-effective screening for the antibiotic resistant bacteria that frequently cause serious hospital acquired infections. Every year, nearly 100,000 deaths result from 2 million serious hospital acquired infections at an estimated cost of $30.5B. About 20,000 of these fatalities are caused by methicillin-resistant Staphylococcus aureus bacteria (MRSA). Both the rate of hospital acquired infections and the spread of MRSA have increased dramatically in the last 30 years. Many individuals now carry MRSA on their bodies, even when healthy. When MRSA carriers are hospitalized the resistant microbe can cause serious infections for the carrier and others in the hospital. Recent studies have shown that hospitals can substantially decrease the occurrence of hospital acquired infections by screening admitted patients for MRSA and then treating them using rigorous infection control procedures including isolation. Traditional microbiological methods for screening patients for MRSA are very slow, requiring several days, and are therefore incompatible with rapid identification and isolation of MRSA carriers. New rapid MRSA tests based on nucleic acid amplification are used for MRSA screening at some sites. However these tests are expensive, complex and thus not currently practical for large scale screening in most hospitals. We aim to develop a novel rapid, sensitive, and easy-to-use system for large scale cost-effective MRSA screening. The system's proprietary technology uses low-cost non-magnified digital imaging to count individual S. aureus cells specifically tagged with highly fluorescent particles. The test determines the initial number of S. aureus cells in the sample and the number of S aureus cells after incubation for several hours in antibiotic-containing selective media. Only if the sample contains MRSA, will there be a significant in- crease in S. aureus cell number in the presence of antibiotic. An advantage of this phenotypic growth-based approach over genotypic nucleic acid-based tests is that it can be applied to any type of microbe and any anti- biotic. The Specific Aims are to (1) develop S. aureus-specific particle reagents and the MRSA screening as- say method;(2) develop an automated prototype system including an imaging instrument and a reagent- containing cartridge;and (3) demonstrate assay performance and compare it to the culture and nucleic acid amplification reference methods using clinical samples. Achieving these Specific Aims should justify a Phase 2 project that will focus on extending the MRSA assay to other sample types (e.g., wound, soft tissue, blood), developing tests for other important agents that cause hospital acquired infection agents (e.g., vancomycin resistant Enterococcus, C. difficile), and developing a pre-commercial prototype instrument/consumable system for MRSA screening. Besides its value for detecting resistant microbes, the system has commercial potential for other important cellular detection applications including detecting virally infected cells, CD4+ cells (for monitoring HIV status), food pathogens, and in drug discovery. PUBLIC HEALTH RELEVANCE The commercialized MultiPath system for screening for resistant bacteria will help lower the rate of hospital acquired infections. The approximately 2 million hospital acquired infections that occur per year cause nearly 20,000 deaths and cost the healthcare system about $30B a year. The new system will enable more hospitals to implement rapid testing, which in turn leads to improved infection control and lower hospital acquired infection rates.